Mullis1

2 Concentration Measurements Molarity = M = moles of solute volume of solution in L molality = m = moles of solute mass of solvent in kg Mole = X = moles of substance S Fraction total moles in solution

Mullis3 Colligative properties van’t Hoff factor = i i = number of ions one unit of substance will dissociate into in solution CaCl 2 dissociates into Ca 2+, Cl - and Cl -, so i= 3. Boiling Point Elevation ΔT = ik b m ΔT = increase in solution boiling point k b = boiling point elevation constant for the solvent m = molality (for now)

Mullis4 Freezing Point Depression ΔT = ik f m ΔT = decrease in solution freezing point k f = freezing point depression constant for the solvent m = molality Vapor Pressure Lowering P = XPº P = vapor pressure of the solution X = mole fraction of the solvent Pº = vapor pressure of the pure solvent Add solute: Solution’s vapor pressure goes down. Lower vapor pressure = Raise boiling point

Mullis5 Solubility Product For the reaction: A a B b (s) a A b+ (aq) + b B a- (aq) The solubility expression is: K sp = [A b+ ] a [B a- ] b Example: The solubility of strontium fluoride in water is 1 x M at room temp. What is the value of its solubility product? [Sr 2+ ] = 1 x M and [F - ] = 2 x M SrF 2  Sr F - so K sp = [Sr 2+ ][F - ] 2 K sp = [1 x M][2 x M] 2 = 4 x 10 -9

Mullis6 Intermolecular forces: Generalizing properties Low boiling point = particles are more likely to leave liquid solution Weaker IM forces = lower boiling point Lower boiling point = more vapor = higher vapor pressure High boiling point = slow evaporation If IM forces are the same, look at formula weight. Heavier molecules have higher boiling points. Strength of IM forces: Hydrogen bond>dipole-dipole>London dispersion

Mullis7 Intermolecular Forces (Chart from Chemistry: The Central Science by Brown-LeMay et al.) Interacting molecules or ions Polar molecules?Ions involved? Are polar molecules and ions both present? Are H atoms bonded to N,O or F atoms? NoYes London Forces only Ex. Ar(l), I 2 (s) No Dipole-Dipole Ex. H 2 S No Hydrogen Bonding Ex. NH 3, H 2 O Yes Ion-dipole Forces Ex. KBr in H 2 O Yes Ionic bonding Ex. NaCl No